Micheál Martin is set to be Taoiseach in a coalition of Fianna Fáil, Fine Gael and the Green Party.
Although with the caveat that this deal needs to get past the memberships of the three parties (and the Greens, I believe, require a two thirds majority, so their membership could easily scupper it).
Anyway, assuming this does go through and the coalition lasts the distance, I assume whoever is UK PM in five years time will be saying hello Mary Lou when he calls to conduct socially distanced negotiations over the future of the Irish border.