Glasgow Warriors tighthead Fagerson has been ruled out of the summer tour to Australia with a calf problem, prompting Farrell to bring in the Canberra-born Bealham, who he's coached when in charge of Ireland.
The news of Fagerson's withdrawal came a day before the squad - minus those involved in Premiership and United Rugby Championship finals - headed out to Portugal for a training camp.
Farrell, though, accepts such situations are part of the game, with the group now looking to sharpen focus towards a warm-up fixture against Argentina in Dublin on June 20.
"It is heartbreaking, but at the same time, he (Fagerson) is a realist. All rugby players know that's the game," Farrell said.
"He will work unbelievably hard to get himself fit and who knows what's going to happen down the track."
On Ireland's Bealham being added to the squad, Farrell said: "Finlay has been called up in his place and he is in good form. He is very good at what he does.
"He was certainly right up there in the conversation from the very start as well, and he would have been disappointed not to make the group.
"So we just know he will be a great fit for the group going forward. He is the only conversation that I was able to have because of the way we did the squad announcement.
"By giving him a phone call and telling him he was selected within the squad, unfortunately for Zander, but it was one of the best phone conversations I have ever had.
"The emotion that went through the phone actually welled me up. It was great to be able to do that."
With 15 of the selected players still on club duty - including 12 from Leinster - England duo Jamie George and Asher Opoku-Fordjour have also joined the five-day training camp at Quinta do Lago to provide some front-row cover.
The fixture against Argentina is set to be a first Lions game played in Ireland.
The tour of Australia schedule - which features three Tests against the Wallabies - begins against Western Force in Perth on June 28.
