He came on as a blood replacement for Brian O'Driscoll in the 67th minute and then stayed on the pitch when the talismanic centre returned, taking over from brother Rob in the 72nd minute.
It meant the two brothers only spent six minutes on the pitch together, but that was enough to write the County Louth family into the history books.
Emphasising the Leinster squad's desire to achieve an historic double in the RaboDirect PRO12 final, Rob said: "First and foremost, we were really disappointed with how last season finished up.
"We put ourselves in a really good position to win the league but failed. But we're grateful for the opportunity we have got ahead of us this week to do something special.
"The PRO12 is our bread and butter tournament. If we achieve a win next week it could be more of a testament to Leinster Rugby.
"The Ospreys turned us over in the final (at the RDS) two years ago and there's still a lot of hurt in the guys from that game."
Before the 17th Heineken Cup final only four sets of brothers had secured winners' medals.
Ulster duo Jan and Bryn Cunningham were the only other Irish pair previously in the record books from 1999, while four-times winners Toulouse provide two sets of brothers from their first success in 1996 and their third in 2005.
HEINEKEN CUP WINNING BROTHERS:
Philippe and Olivier Carbonneau (Toulouse, 1996)
Jan and Bryn Cunningham (Ulster, 1999)
Martin and Will Johnson (Leicester Tigers, 2001 and 2002)
Isitolo and Finau Maka (Toulouse, 2005)
Rob and David Kearney (Leinster, 2012)