Rane and his two sons BJP candidate from Kankavali Nitesh and former Congress MP Nilesh formally joined the ruling party, as the Sena was left fuming.
Going a step further, Fadnavis also addressed an election rally in favour of Nitesh Rane, who was the sitting Congress MLA before he quit the party recently, leaving many red faces in the Sena which had bitterly opposed the CM's visit to Kankavali last week.
A massive tug-of-war was witnessed between the two allies over the past few days with the Ranes proclaiming Fadnavis would come to campaign in Kankavali, and the Sena's ministers including Desai dismissing it.
"All eyes were on this (merger) for a long time... It has finally happened today. There is hardly any competition here... The BJP will benefit hugely with the Ranes... entry to the party," Fadnavis said, cocking a snook at the Sena which has given a ticket to Satish Sawant and vowed to teach Nitesh Rane a "lesson".
He said journalists often asked when "Rane Saheb" is joining a few day ago Nitesh joined, today Nilesh joined, "Rane Saheb is already a Rajya Sabha Member and also our member," Fadnavis said amidst a huge round of applause.
The BJP-MSP merger would have a bearing on the political dynamics of the coastal Konkan region which is considered a support base of the Sena.
The aggressive Rane Sr. served as the CM for almost a year during the latter part of Sena-BJP alliance government 1995-1999, and after it lost power to the Congress-NCP, he became the Leader of Opposition.
However, in July 2005, the late Sena patriarch Bal Thackeray expelled him from the party for revolting against Uddhav Thackeray's authority.
Undaunted, Rane joined the Congress, became a minister for several years, but was consistently sidelined for his claim to the CM's post or the state party chief, as he was perceived to be a political threat to the Maratha lobbies in both the Congress and NCP.
Disheartened, he quit the Congress in September 2017 to float the MSP, which allied with the NDA, and was supported by the BJP for a Rajya Sabha nomination, and now his party has merged with the BJP, days before the October 21 Assembly elections.
( With inputs from IANS )